This invention relates to an improved spouted bed device, and more particularly, to an electric field coupled spouted bed device and a method for controlling the spout inlet conditions thereof.
A related copending application is application Ser. No. 194,630 filed Oct. 6, 1980, which is assigned to the same assignee as that of the present application.
Spouted bed devices are widely employed in material processing operations such as grain drying, tablet coating, pneumatic transport, and in chemical reaction systems. The basic design and operation of spouted bed devices is well known in the art as evidenced by numerous publications including Spouted Beds, K. B. Mathur and N. Epstein, Academic Press, New York, 1974. An exemplitive spouted bed device is described in U.S. Pat. No. 2,786,280 (Gishler et al) which is incorporated herein by reference.
Conventional spouted bed devices typically include a bed of granular material into which a jet of fluid such as air is directed to form a spout in which a portion of the granular material is entrained. These conventional devices offer little control flexibility since variable parameters such as fluid flow rate and bed height are dependent on the properties of a given bed material. Accordingly, these parameters can only be varied within a narrow range, if at all.
More recently, pipe inserts or "draft tubes" have been positioned in the bed region above the vessel fluid inlet to force a large percentage of the fluid to travel up through the bed without diffusing therein, except in a spout inlet region between the fluid inlet and the draft tube inlet. In this manner the minimum fluid flow rate required for useful operation of a spouted bed device with a given bed material is reduced, allowing a somewhat greater operational flexibility. However, variable control remains limited over spout inlet conditions which can directly affect any associated material processing operation.
For example, the recirculation rate of bed material is potentially variable as a function of the fluid flow rate at the spout inlet. However, the minimum flow rate required for spouting in such a device with a given bed material can be varied only by physically adjusting the separation distance between the fluid and draft tube inlets, which is a rather complicated task. Additionally, as the flow rate is increased a greater percentage of the fluid diffuses and inefficiently bypasses the draft tube inlet. Further increases in the flow rate results in additional flow bypassing which may disrupt the solids movement in the granular bed with a corresponding loss of process control.
Accordingly, it is an object of the present invention to provide a means and a method for variably controlling processes carried out in a spouted bed device.
It is also an object of the present invention to provide an improved means for controlling the recirculation rate of granules in a spouted bed device.
It is a further object of the present invention to provide a means for channeling fluid from a fluid inlet into a draft tube of a spouted bed device upon an increase in the fluid flow rate.
Another object of the present invention is to enable the control of the solids delivery rate for a pneumatic transport system.
Still another object of the present invention is to provide a spouted bed device that may be employed with a variety of granular materials and fluid flow rates without requiring modifications to the geometry thereof.